In drilling operations, it is common to use sacrificial or consumable parts in high wear areas. One such area is the drill string assembly. The drill string assembly usually comprises a lesser expensive consumable known as a sub adaptor, which connects the typically more expensive drill spindle to other drill string elements such as a drill bit or drill extension stem. The drill spindle must, in use, operate in forward and reverse, without the sub adaptor uncoupling from the drill spindle.
There have been many ways of locking the sub adaptor to the drill spindle, including: welding tabs between the sub adaptor and spindle. However, these methods often involve damaging the more expensive drill spindle, potential electric shock to welding operators, the need for skilled labour, thread leakage while drilling, and other disadvantages.
The present invention seeks to alleviate one or more of the above mentioned disadvantages.